1. Field of the Invention
The present invention relates to a pulse shaping system, a laser printer, a pulse shaping method and a method of generating serial video data for a laser printer. More particularly, the present invention relates to a pulse shaping system suitable for generating video signals for a laser printer, a laser printer, a pulse shaping method and a method of generating serial video data for a laser printer.
2. Description of the Prior Art
Previously disclosed technique for enabling a laser printer to print pictures in high picture quality controls the output of a laser at a resolution higher than that of a printer engine. The technique provides serial data of a resolution higher than 1 bit for one dot provided by a printer engine, and controls the output of the laser using the serial data of high resolution to print one dot in a delicate tone. The high-resolution serial data is generated by a pulse shaping system and has a resolution higher than a predetermined video clock. For example, a resolution on the order of 1/64 is required when the resolution of a printer engine is 600 dpi to print pictures in a satisfactory picture quality by a color laser printer.
The aforesaid prior art technique needs a high-frequency clock generating circuit capable of generating a clock signal of, for example, 1344 MHz (672 MHz when both the leading and the trailing edge are used) to achieve a high resolution of 1/64 for a video clock signal of 21 MHz. Conventionally, a high-performance modulation IC that modulates frequency by frequency division using a PLL or the like is used. This modulation IC, however, is an expensive large-scale circuit.